ES2411915T3 - Procedure for the conditioning of a waste solution containing organic substances and metals in ionic form that are produced in the chemical wet cleaning of conventional or nuclear facilities. - Google Patents

Abstract

Procedure for conditioning a waste solution from wet cleaning of conventional installations or nuclear technology, which contains at least one organic substance and at least one metal in ionic form, where at least a part of the Organic substance is broken down by an electrochemical treatment of the waste solution, and precipitates at least one metal by the addition of phosphoric acid, and the phosphate precipitate that appears is removed from the waste solution.

Description

Procedure for the conditioning of a waste solution containing organic substances and metals in ionic form that are produced in the chemical cleaning by wet of conventional or 5 nuclear facilities.

The invention relates to a process for the conditioning of a waste solution containing organic substances and metals in ionic form that are produced in the chemical cleaning by wet of conventional or nuclear facilities. Said solutions are formed when, for example, in the secondary cleaning of steam generators of nuclear power plants, deposits containing magnetite are eliminated. For

For this purpose, cleaning solutions are used, which for example contain at least one organic agent that forms a water-soluble complex with metal ions such as Fe-II and / or Fe-III, for example, an organic acid such as EDTA. After finishing the cleaning, waste solutions are obtained, which contain the said complex compounds as well as possibly part of the unused organic agent. In addition, they may also contain other organic compounds such as amines and inorganic compounds, for example nitrate ions and

15 ammonium ions The value CSB is usually used as a measure for the content of organic substances. This value gives the chemical need for oxygen (Chemischen Sauerstoffbedarf) that is necessary for the degradation of organic substances in CO2 and water. This type of waste solutions, because they generally contain a high metal content and CSB value,

20 need an environmentally friendly disposal. In the case of non-radioactively contaminated solutions, some countries, such as Germany, allow disposal by incineration as hazardous waste. When the waste solution is radioactively contaminated, which for example can happen in the cleaning of the steam generator of nuclear power plants, or an incineration of non-radioactive waste solutions is not allowed, this type of procedure does not come into question. In a procedure

During conditioning, the organic components decompose completely ideally, electrochemically in carbon dioxide and water. For the removal of metal ions from the solution, this is carried out by ion exchangers. In this regard, considerable amounts of exchange resins are produced, charged, eventually radioactively contaminated, as a secondary waste, which must be stored or disposed of in an extraordinarily expensive manner. In the exchange resins,

30 loaded with metals, the ratio of volumes between the exchange resin and the volume or respectively the mass of metal ions is extremely unfavorable.

As a result, the invention assumes the task of proposing a procedure with which a waste solution of the class cited at the beginning is simply and economically conditioned.

This task is solved by a procedure according to claim 1 and a procedure according to the

Claim 4. In the first mentioned process, at least a part of the organic substances is degraded by electrochemical treatment of the waste solution, and at least one metal precipitates by the addition of phosphoric acid, and the phosphate precipitate Appeared is removed from the waste solution. The method described in claim 4 differs in that the metals obtained in the waste solution are not broken down by an electrochemical process but by a UV light treatment.

40 Based on an electrochemical treatment or irradiation with UV light, the organic compounds are finally decomposed into CO2 and water. Complex metal compounds release these only in the course of the decomposition of their metal ions bound to the metal complex. In both variants of the procedure it is advisable to work in acid solution until weakly basic, namely, in a pH range of approximately

45 3 to 9, since the formation of metal hydroxides precipitates is avoided or decreased. The precipitates appearing in the alkaline margin settle very slowly and can only be separated very hard, for example, by filtration. In a very different way, the phosphate precipitate behaves. These are not very bulky and can be separated with little disbursement of technical devices, without problems, by filtration or centrifugation. On the contrary, in a separation with an ion exchanger takes place in this

50 process an obviously smaller volume of waste. The phosphoric acid used for the precipitation of the metal also has the advantage that simultaneously it can be used to adjust the said pH value range (pH of approximately 3 to 9), and mainly since it is an oxyacid, it produces an acceleration. of the degradation of organic compounds. From a

Oxidized or respectively, from the corresponding acid radical (phosphate) are formed in the anode, peroxy compounds (peroxyphosphates), which as very strong oxidation agents accelerate the oxidative decomposition of the organic substances in carbon dioxide and water. The phosphoric acid used according to the invention, which forms very difficult soluble precipitates with many metals such as, for example, iron, cobalt or nickel, guarantees on the one hand a smooth separation of many metals from the waste solution, in

60 particular of iron, and on the other hand an acceleration of the degradation process.

In the electrochemical decomposition, known per se, of organic substances in aqueous solution, oxyacids were used, for example sulfuric acid only as regards acceleration of degradation. A precipitation reaction in this regard was not planned. Due to the very fast reaction

5 between metal ions and phosphate ions, as well as the rapid formation of precipitate, as will be clarified in more detail below, turbulence and other adverse effects, at least, decrease.

In the case of the UV variant of the process, a strong oxidizing agent such as hydrogen peroxide is added for acceleration of degradation.

In both versions of the process it can be conceived first to effect the degradation of the substances

10 organics contained in the waste solution to the desired extent, and then cause, by the addition of phosphoric acid, the precipitation of metals. In both versions of the procedure it is, however, advantageous to start with the precipitation first, and in particular from the beginning, that is, at a time when the organic substances of the content are not yet completely destroyed or respectively are not the desired measure. In both versions of the procedure the effectiveness of the procedure will increase,

15 as described below in detail.

The practical execution of the procedure is possible with a relatively small technical outlay. The waste solution to be treated is electrolyzed in an appropriate tank, or it is irradiated with UV light, until the organic substances are completely degraded or to a tolerable residual amount. In the case of an electrolytic treatment, at least one diamond electrode is used to suppress the possible annoying formation of oxygen and enable the appearance of strongly oxidizing peroxides compounds (of oxy compounds, in particular phosphoric acid). When the waste solution is an already used cleaning solution, which has been used for cleaning the steam generator of a nuclear power plant, then that solution contains a large amount of iron that comes from the magnetite deposits of the steam generator. For the elimination of this deposit, the cleaning solution contains an organic complexer such as EDTA. In order to prevent an attack on the metal material of the steam generator during cleaning 25, as a rule steel, an alkaline medium is used, that is, the cleaning solution contains an alkalizing agent such as ammonia or ammonium ions or morpholino In addition, the cleaning solution contains a reducing agent such as hydrazine to prevent an oxidizing attack on the steam generator material. After cleaning, the iron that is present, mainly in the form of a divalent iron complex, is dissolved in the form of an iron complex, for example as an EDTA complex. Together with iron, other materials such as cobalt or nickel may be present in a small amount of waste in this class. Among them may also be present, radionuclides that due to small leaks have been deposited on the secondary face of the steam generator. In the cleaning of a steam generator large quantities of cleaning solutions already used are produced, approximately in the range of some hundreds of 35 cubic meters, for example 2 m3. So that this kind of quantities can be treated in the cleaning solution with a reasonable cost of time, electrodes are used in the form of plates, of a porous material. The electrode plates in this respect have a surface for example from 2� m2 to 4� m2. The electrode plates or their outer surfaces and also their inner surface, are provided with a thin layer of diamond. The duration of the procedure depends on the corresponding load of the solution of

40 residues of organic substances, the surface of the electrodes and the current density.

In a waste solution of the aforementioned class, a pH value is used, with which the precipitation of a metal hydroxide is avoided or at least decreases. This is the case of a pH value from approximately 3 to 9. In addition to the hydroxide precipitates being difficult to separate from the waste solution, they have the additional disadvantage that they are deposited on the surface of the electrodes, and hinder their operation and the one with 45 UV rays. A work in acid solution is preferred, since the formation of a difficultly filterable metal hydroxide precipitate can be effectively inhibited. In addition, phosphoric acid is added to the solution in an amount sufficient to precipitate the metals contained in the solution, namely, iron. In this regard, stoichiometric preference amounts of phosphoric acid are used, since an excess thereof does not produce any effect on precipitation, and only the secondary residue would increase. For one mole of iron, which corresponds to a mass of, g, one mole or 9 g of phosphoric acid is necessary. The added phosphoric acid causes acidification of the solution, so that most of the time no additional measures are necessary to adjust the pH value. During electrolysis or irradiation with UV rays, all organic components, among which are also complexing agents, for example, EDTA, are broken down into carbon dioxide and water. Iron, which is present, for example, in a range in the range of g / liter up to 4 g / liter, is released, so that it can bind with phosphoric acid phosphate radicals, which accumulate together with the precipitate at the bottom of the container. The iron phosphate and also the hardly soluble phosphates of other metals settle rapidly and can be separated from the solution without problems, preferably by filtration or by centrifugation. This way it is removed from the

waste solution, practically the total metal content, including any radionuclides present. The remaining solution contains at most only traces of organic compounds and impurities not completely decomposed, which can be removed in a conventional manner, for example by evaporation or combustion. Separate phosphates can be conducted as hazardous wastes for

5 take the corresponding disposal measures. In the case of a radioactive contamination, these wastes are eventually passed, after integration into a solid matrix of binder, to a corresponding final storage or to a provisional storage.

The addition of phosphoric acid in question can be done in principle, at any time during the procedure. However, it has been surprisingly shown that the process works effectively when phosphoric acid is present from the beginning, or respectively, when added during electrochemical treatment. During the processing of the waste solutions, it was used at the beginning and in one case, towards the end of the procedure. The waste solutions contained comparable amounts of EDTA, morpholine, hydrazine and unused iron. The total content of organic substances corresponded to a chemical need for oxygen or, respectively, a CSB value from 32� mg of 02 / liter to 3 mg of 02 / liter. The waste solutions 15 were treated each time with diamond electrodes in the form of plates with a geometric surface of 3 m2, of the class described above. During the treatment, at certain intervals of time, the iron content and the specific load applied each time were determined. In the diagram attached below, the iron content versus the specific load is represented. It can be observed that in the cases of an addition to the principle of phosphoric acid in a stoichiometric amount with respect to the iron content, in a total loading amount of 1 Ah / l of the iron content of the beginning of 11�� mg / liter or respectively 13� mg / liter decreased to values below 1� mg / liter (see the diagram each time the curves marked with the measuring points in the form of triangles and in the form of small circles). In the event that, on the contrary, the phosphoric acid was added only at the end of the procedure, (also with a stoichiometric amount versus the iron content), that is, when a charge of approximately 1� Ah / has already been supplied. liter, it was shown that after the phosphate precipitation an essentially higher iron content remained, a content of approximately 11� mg / liter, in the waste solution (see the diagram for the curve with the measured measurement points in the form of squares). In the event that the phosphoric acid is already present from the beginning, the free iron will join immediately and precipitate as iron phosphate. It is deposited relatively quickly in the bottom of the reaction vessel, so that the danger of deposition on the surfaces of

30 electrodes is very small. In the absence of phosphoric acid, on the contrary, depositions are formed containing iron on the electrodes, which have a disadvantageous influence on the effectiveness of the electrodes and precipitation.

The decomposition of the organic substances of the content of a waste solution can also be carried out instead of, or in addition to, an electrochemical treatment by irradiation with UV rays. Through

In irradiation with UV rays in combination with an oxidation agent such as hydrogen peroxide, organic substances also degrade essentially in carbon dioxide and water. Next to this, metals bound to complexes are released, so that they can be precipitated and separated in the manner described above.

In the case of a wastewater treatment with the help of UV irradiation, it is

It is also advantageous to carry out an initial addition of phosphoric acid, in particular with respect to the aforementioned effect of the coating of the reaction surface of the UV lamps with deposits containing iron. It has been observed that when the irradiation was carried out with UV rays without the presence of phosphoric acid, or when it was only added late, there was a turbidity of the solution, which led to a reduction in the yield of the UV rays.

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Claims (5)

1. Procedure for the conditioning of a waste solution from wet cleaning of conventional facilities or nuclear technology, which contains at least one substance 5 organic and at least one metal in ionic form, where at least a part of the organic substance is disintegrated by an electrochemical treatment of the waste solution, and at least one metal precipitates by the addition of phosphoric acid, and The phosphate precipitate that appears is removed from the waste solution. Method according to claim 1, in which for the electrochemical treatment, an anode with an oxygen surge is used.

3.

Method according to claim 1 or 2, in which another oxicomposite is contained in the waste solution together with the phosphoric acid.

Four.

Procedure for the conditioning of a waste solution produced in chemical cleaning, conventional or nuclear facilities, containing at least one organic substance and at least one metal in ionic form, in which at least one part of the organic substance, disintegrates from the waste solution by irradiation with UV rays, and at least

A metal precipitates by the addition of phosphoric acid, and the phosphate precipitate that appears is removed from the waste solution. . Process according to one of the preceding claims, in which, in front of at least one organic substance, an effective oxidizing agent is added to the waste solution. . Process according to the claim, in which, as an oxidizing agent, hydrogen peroxide is added to the waste solution. �. Method according to one of the preceding claims, in which the phosphoric acid is added at a time in which at least one organic substance is not yet completely disintegrated. . Procedure according to claim �, in which the phosphoric acid is added at the beginning. 9. Method according to one of the preceding claims, in which the phosphoric acid is added in a stoichiometric amount with respect to the metal content. 1. Method according to one of the preceding claims, in which a pH value from 3 to 9 is adjusted in the waste solution. Method according to one of the preceding claims, which is used for the treatment of waste solutions containing iron. 12. Method according to one of the preceding claims, which is used for the conditioning of a waste solution, which contains an organic complex compound of a metal.